In vacuum skin packaging, a product to be packaged is placed on a product supporting member. The product serves as the mold for a thermoformable polymeric film. The thermoformable film is formed about the product by means of differential air pressure. However, the term "vacuum skin packaging" (hereinafter, "VSP") refers to not only the fact that the thermoformable film is formed around the product by vacuum or differential air pressure, but also to the fact that the product is packaged under vacuum, with the volume containing the product being evacuated during the packaging.
In conventional skin packaging, a porous or perforated backing board is employed, so that a vacuum may be drawn directly through the backing board. However, vacuum skin packaging processes generally use a vacuum chamber with an open top. The product (on an impermeable backing board through which vacuum is not drawn), is placed on a platform within the vacuum chamber. The top of the chamber is covered by a sheet of film which is clamped tightly against the chamber to form an air-tight closure. The chamber is evacuated while the film is heated to its forming and softening temperature. The platform is then raised to drive the product into the softened film, and air pressure can be used about the film to force it tightly around the product.
In vacuum skin packaging, it is also known to release the vacuum and allow ambient air into the chamber, after the chamber has been evacuated and the product driven into the heat-softened film, or vice versa. In this manner, the thermoplastic film molds more or less over and against the product, since there is a vacuum inside the package, and ambient air pressure, or more than ambient air pressure, immediately outside of the package.
Also known are packages for meats, which include an inner O.sub.2 -permeable film and an outer O.sub.2 -impermeable film, with the package being either gas flushed or evacuated. For marketing, the outer O.sub.2 -impermeable member is removed and the inner package is displayed at the meat counter for the consumer. Being O.sub.2 -permeable, the inner wrapper admits O.sub.2 to the interior of the package, causing the fresh meat product to change to a bright red color, i.e., "bloom", which the consumer associates with freshness. The inner film of the package is a polyethylene film, and the outer film may be cellophane film with a coating of saran (vinylidene chloride copolymer, i.e., "PVDC"). Peelable outer O.sub.2 -impermeable films are known for use on such packages.
It is known to flush a package with O.sub.2 gas in order to provide the desired bright red "bloom" of the meat. However, at locations where the O.sub.2 -impermeable film (i.e., an oxygen barrier film) prevents O.sub.2 from access to the surface of the meat, the meat becomes discolored due to the lack of O.sub.2 available to bloom the meat.
It would be desirable to develop an O.sub.2 -impermeable package comprising a meat product, in which the meat product did not become discolored due to a lack of O.sub.2 caused by one or more O.sub.2 -impermeable components in relatively close proximity to the meat. For example, in the packaging of a 1 inch thick beef steak on a 0.7 inch deep polystyrene foam tray, it would be desirable to provide a high oxygen atmosphere within the package to keep the meat bloomed in order to both extend shelf life and maximize the appearance to the customer.
Furthermore, even having two films over the meat, i.e., an O.sub.2 -permeable film over the meat and in direct contact with the meat, and an O.sub.2 -impermeable film over the O.sub.2 -permeable film, without more, does not solve the problem, i.e., the surface of the meat does not remain bloomed because gaseous oxygen cannot reach the surface of the meat.